From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/5] ARM: tegra20: cpuidle: add powered-down state for secondary CPU
Date: Mon, 03 Dec 2012 11:31:58 -0700 [thread overview]
Message-ID: <50BCF01E.4070504@wwwdotorg.org> (raw)
In-Reply-To: <1354503607-13707-2-git-send-email-josephl@nvidia.com>
On 12/02/2012 08:00 PM, Joseph Lo wrote:
> The powered-down state of Tegra20 requires power gating both CPU cores.
> When the secondary CPU requests to enter powered-down state, it saves
> its own contexts and then enters WFI. The Tegra20 had a limition to
> power down both CPU cores. The secondary CPU must waits for CPU0 in
> powered-down state too. If the secondary CPU be woken up before CPU0
> entering powered-down state, then it needs to restore its CPU states
> and waits for next chance.
>
> Be aware of that, you may see the legacy power state "LP2" in the code
> which is exactly the same meaning of "CPU power down".
> diff --git a/arch/arm/mach-tegra/sleep-tegra20.S b/arch/arm/mach-tegra/sleep-tegra20.S
> +/*
> + * tegra_pen_lock
> + *
> + * spinlock implementation with no atomic test-and-set and no coherence
> + * using Peterson's algorithm on strongly-ordered registers
> + * used to synchronize a cpu waking up from wfi with entering lp2 on idle
> + *
> + * SCRATCH37 = r1 = !turn (inverted from Peterson's algorithm)
A link to a description of that algorithm would be useful.
> + * on cpu 0:
> + * SCRATCH38 = r2 = flag[0]
> + * SCRATCH39 = r3 = flag[1]
> + * on cpu1:
> + * SCRATCH39 = r2 = flag[1]
> + * SCRATCH38 = r3 = flag[0]
That implies that r2/r3 are used for different purposes on the 2 CPUs,
and/or shadow the values of different registers. However, I see nothing
in the code which is conditional on cpu ID.
next prev parent reply other threads:[~2012-12-03 18:31 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-03 3:00 [PATCH 0/5] ARM: tegra20: cpuidle: add power-down state Joseph Lo
2012-12-03 3:00 ` [PATCH 1/5] ARM: tegra20: cpuidle: add powered-down state for secondary CPU Joseph Lo
2012-12-03 18:18 ` Stephen Warren
2012-12-04 6:47 ` Joseph Lo
2012-12-03 18:31 ` Stephen Warren [this message]
2012-12-04 7:05 ` Joseph Lo
2012-12-05 18:36 ` Stephen Warren
2012-12-03 3:00 ` [PATCH 2/5] ARM: tegra20: clocks: add CPU low-power function into tegra_cpu_car_ops Joseph Lo
2012-12-03 18:20 ` Stephen Warren
2012-12-04 4:28 ` Joseph Lo
2012-12-04 5:12 ` Prashant Gaikwad
2012-12-04 5:25 ` Joseph Lo
2012-12-05 18:34 ` Stephen Warren
2012-12-03 3:00 ` [PATCH 3/5] ARM: tegra20: flowctrl: add support for cpu_suspend_enter/exit Joseph Lo
2012-12-03 3:00 ` [PATCH 4/5] ARM: tegra20: cpuidle: add powered-down state for CPU0 Joseph Lo
2012-12-03 18:40 ` Stephen Warren
2012-12-04 7:25 ` Joseph Lo
2012-12-03 3:00 ` [PATCH 5/5] ARM: tegra20: cpuidle: apply coupled cpuidle for powered-down mode Joseph Lo
2012-12-03 18:52 ` Stephen Warren
2012-12-04 10:20 ` Joseph Lo
2012-12-04 12:41 ` Peter De Schrijver
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